10G Ethernet issue on Mac mini 2024 with M4

This was posted as an answer to an existing thread, but It is probably better to create a separate thread for it.

I have a problem with the M4 equipped with a 10G interface which can not operate at 10G speed, it works very well at 1G, but can't seem to work more than few seconds when speed is set to 10G (we are network experts, with +20y of expertise in Linux / BSD networking).

Problem can be described as follow:

1. Context:

• MacMini 2024 with 10G Ethernet option - 15.2 (24C101)
• Connected to a 10G fiber switch - FS switch: S3900-24T4S-R - latest firmware
• Proper 10G transceiver (Ethernet >> fiber)
• Switch port known to work with 10G fiber

2. Problem:

• speed auto-select does not work (fall back to 1G)
• forcing speed to 10GbaseT allows interface to switch to 10G for few seconds (interface is up and can ping with no pb).
• after a "few seconds" (random) interface disconnects / reconnects randomly and finally stays down
• changing flow control or other settings does not solve the issue
• only way to "solve" the issue is to lower port speed which is "not ok at all"

Cable is brand new cat. 6A (have bought one specially for this) and of course compatible with 10G speed.

I suspect a firmware problem with the 10G Apple interface -- not sure which manufacturer is behind this, probably some low end manufacturer… 

Does anyone have any clue on how to solve this ?

I have seen couple of threads related to this, so I don't think I am the only one with this pb.

[Re-Titled by Moderator]